Because of their low cost, light weight and ease of manufacture, polymeric (plastic) components are rapidly replacing metal components in a wide variety of contexts ranging from shoehorns to automobile components. Notably, the development of high strength, impact resistant plastics and the ability to provide scratch and scuff resistant high gloss surface finishes plastics are replacing metal components in many contexts where the components are subject to considerable mechanical forces. Thus, for example, plastic components are being used with increasing frequency as bearings, automobile body panels, bumpers, and the like.
Plastics are frequently overcoated with various compositions to achieve particular surface properties. Such overcoatings include, but are not limited to, acrylic paints to provide color and a high-gloss finish, metallic or ceramic plating compositions, lubricants, adhesives, anti-fog compositions, and the like.
Achieving effective overcoating of a plastic typically requires that the overcoating composition easily wet the underlying plastic. Especially where the plastic is non-polar (e.g. ABS, polyethylene, polypropylene, etc.) the plastic is often activated to produce a wettable surface and/or to provide reactive sims for the bonding of the overcoating.
Plastic surface activation is accomplished by a wide number of means well known to those of skill in the art including corona discharge, radio-frequency exposure, microwave exposure, plasma treatment, microwave-plasma treatment and various chemical methods. Once activated, the surface must typically be overcoated relatively rapidly. Any soiling, e.g. by dirt, grease, oil or other materials may interfere with the even coating and bonding of the overcoating composition. In addition, the surface may only remain activated for a short period of time as the activated functional groups in the plastic may react with any chemical species (e.g., oxygen) in the immediate environment. Finally, particularly where the overcoating provides mechanical protection (e.g. hardness, scuff resistance, etc.) the overcoating must be applied before the vulnerable underlying plastic suffers any mechanical damage.